A | B | C | D | E | F | G | H | CH | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
A heat wave[1] (or heatwave[2]), sometimes described as extreme heat, is a period of abnormally hot weather.[3]: 2911 Definitions vary but are similar.[4] A heat wave is usually measured relative to the usual climate in the area and to normal temperatures for the season.[3]: 2911 Temperatures that humans from a hotter climate consider normal, can be regarded as a heat wave in a cooler area. This would be the case if the warm temperatures are outside the normal climate pattern for that area.[5] High humidity often occurs during heat waves as well. This is especially the case in oceanic climate countries. Heat waves have become more frequent, and more intense over land, across almost every area on Earth since the 1950s. Heat waves occur from climate change.[6][7]
Heat waves form when a high-pressure area in the upper atmosphere strengthens and remains over a region for several days up to several weeks.[8] This traps heat near the earth's surface. It is usually possible to detect heat waves by using forecasting instruments. This allows the authorities to issue a warning.
Heat waves have an impact on the economy. They can reduce labour productivity, disrupt agricultural and industrial processes and damage infrastructure.[9][10] Severe heat waves have caused catastrophic crop failures and thousands of deaths from hyperthermia. They have increased the risk of wildfires in areas with drought. They can lead to widespread electricity outages because more air conditioning is used. A heat wave counts as extreme weather. It poses danger to human health, because heat and sunlight overwhelm the thermoregulation in humans.
Definitions
| Part of a series on |
| Weather |
|---|
 Weather portal |
There are several definitions of heat waves:
- The IPCC defines heatwave as "a period of abnormally hot weather, often defined with reference to a relative temperature threshold, lasting from two days to months."[11][3]: 2911
- A definition based on the Heat Wave Duration Index is that a heat wave occurs when the daily maximum temperature of more than five consecutive days exceeds the average maximum temperature by 5 °C (9 °F), the normal period being 1961–1990.[12] The same definition is used by the World Meteorological Organization.[13]
- A definition from the Glossary of Meteorology is:[14] "A period of abnormally and uncomfortably hot and usually humid weather."
Definitions by country
Europe
Denmark defines a national heat wave (hedebølge) as a period of at least 3 consecutive days in which the average maximum temperature across more than half the country exceeds 28 °C (82.4 °F). The Danish Meteorological Institute also has a definition for a "warmth wave" (varmebølge). It defines this using the same criteria for a 25 °C (77.0 °F) temperature.[15] Sweden defines a heat wave as at least five days in a row with a daily high exceeding 25 °C (77.0 °F).[16]
In Greece, the Hellenic National Meteorological Service defines a heat wave as occurring over three consecutive days with temperatures at 39 °C (102 °F) or higher. In the same period the minimum temperature is 26 °C (79 °F) or more. During this period, there are either no winds or only weak winds. These conditions occur in a broad area.
The Netherlands defines a heat wave as a period of at least five consecutive days in which the maximum temperature in De Bilt exceeds 25 °C (77 °F). During this period the maximum temperature in De Bilt must exceed 30 °C (86 °F) for at least three days. Belgium also uses this definition of a heat wave with Ukkel as a reference point. So does Luxembourg.
In the United Kingdom, the Met Office operates a Heat Health Watch system. This places each Local Authority region into one of four levels. Heat wave conditions occur when the maximum daytime temperature and minimum nighttime temperature rise above the threshold for a particular region. The length of time above that threshold determines the level. Level 1 represents normal summer conditions. Level 2 occurs when there is a 60% or higher risk that the temperature will be above the threshold levels for two days and the intervening night. Level 3 arises when the temperature has been above the threshold for the preceding day and night, and there is a 90% or higher chance that it will stay above the threshold in the following day. Level 4 is triggered if conditions are more severe than those of the preceding three levels. Each of the first three levels gives rise to a particular state of readiness and response by the social and health services. Level 4 involves a more widespread response.[17] The threshold for a heat wave occurs when there are at least three days above 25 °C (77 °F) across much of the country. Greater London has a threshold of 28 °C (82 °F).[18]
Other regions
In the United States, definitions also vary by region. They usually involve a period of at least two or more days of excessively hot weather.[19] In the Northeast, a heat wave typically when the temperature reaches or exceeds 90 °F (32.2 °C) for three consecutive days. This is not always the case. This is because the high temperature ties in with humidity levels to determine a heat index threshold.[20] The same does not apply to drier climates. A heat storm is a Californian term for an extended heat wave. Heat storms occur when the temperature reaches 100 °F (37.8 °C) for three or more consecutive days over a wide area (tens of thousands of square miles).[21] The National Weather Service issues heat advisories and excessive heat warnings when it expects unusual periods of hot weather.
In Adelaide, South Australia, a heat wave is five consecutive days at or above 35 °C (95 °F), or three consecutive days at or over 40 °C (104 °F).[22] The Australian Bureau of Meteorology defines a heat wave as three or more days of unusual maximum and minimum temperatures.[23] Before this new Pilot Heatwave Forecast there was no national definition for heat waves or measures of heat wave severity.[23]
Observations
It is possible to compare heat waves in different regions of the world with different climates thanks to a general indicator that appeared in 2015.[27] With these indicators, experts estimated heat waves at the global scale from 1901 to 2010. They found a substantial and sharp increase in the number of affected areas in the last two decades.[28]
One study in 2021 investigated 13,115 cities. It found that extreme heat exposure of a wet bulb globe temperature above 30 Celsius tripled between 1983 and 2016, and if the effect of population growth (increasing the urban heat island effect) during those years is excluded, the exposure increased a further 50%. The researchers compiled a comprehensive list of past urban extreme heat events.[29][30]
Causes
Heat waves form when a high pressure area at an altitude of 10,000–25,000 feet (3,000–7,600 metres) strengthens and remains over a region for several days and up to several weeks.[8] This is common in summer in both the Northern and Southern Hemispheres. This is because the jet stream 'follows the sun'. The high pressure area is on the equator side of the jet stream in the upper layers of the atmosphere.
Weather patterns are generally slower to change in summer than in winter. So, this upper level high pressure also moves slowly. Under high pressure, the air sinks toward the surface. It warms and dries adiabatically. This inhibits convection and prevents the formation of clouds. A reduction of clouds increases the shortwave radiation reaching the surface. A low pressure area at the surface leads to surface wind from lower latitudes that brings warm air, enhancing the warming. The surface winds could also blow from the hot continental interior towards the coastal zone. This would lead to heat waves on the coast. They could also blow from high towards low elevations. This enhances the subsidence or sinking of the air and therefore the adiabatic warming.[31][32]
In the eastern regions of the United States a heat wave can occur when a high pressure system originating in the Gulf of Mexico becomes stationary just off the Atlantic Seaboard. Hot humid air masses form over the Gulf of Mexico and the Caribbean Sea. At the same time hot dry air masses form over the desert Southwest and northern Mexico. The southwest winds on the back side of the high continue to pump hot, humid Gulf air northeastwards. This results in a spell of hot and humid weather for much of the eastern United States and into southeastern Canada.[33]
In the Western Cape Province of South Africa, a heat wave can occur when the low-pressure area offshore and the high-pressure area inland combine to form a bergwind. The air warms as it descends from the Karoo interior. The temperature will rise about 10 Celsius from the interior to the coast. Humidity is usually very low. The temperature can be over 40 Celsius in summer. The highest temperature recorded in South Africa (51.5 Celsius) occurred one summer during a berg wind along the Eastern Cape coastline.[34][35]
The level of soil moisture can intensify heat waves in Europe.[36][37] Low soil moisture leads to a number of complex feedback mechanisms. These in turn can result in increased surface temperatures. One of the main mechanisms is reduced evaporative cooling of the atmosphere.[36] When water evaporates, it consumes energy. So, it will lower the surrounding temperature. If the soil is very dry, then incoming radiation from the sun will warm the air. But there will be little or no cooling effect from moisture evaporating from the soil.
Climate change
Heatwaves over land have become more frequent and more intense in almost all world regions since the 1950s, due to climate change. Heat waves are more likely to occur simultaneously with droughts. Marine heatwaves are twice as likely as they were in 1980.[38] Climate change will lead to more very hot days and fewer very cold days.[39]: 7 There are fewer cold waves.[40]: 8
Experts can often attribute the intensity of individual heat waves to global warming. Some extreme events would have been nearly impossible without human influence on the climate system. A heatwave that would occur once every ten years before global warming started now occurs 2.8 times as often. Under further warming, heatwaves are set to become more frequent. An event that would occur every ten years would occur every other year if global warming reaches 2 °C (3.6 °F).[41]Impacts on human health
Heat illness is a spectrum of disorders due to increased body temperature. It can be caused by either environmental conditions or by exertion. It includes minor conditions such as heat cramps, heat syncope, and heat exhaustion as well as the more severe condition known as heat stroke.[42] It can affect any or all anatomical systems.[43] Heat illnesses include:[44][45] heat stroke, heat exhaustion, heat syncope, heat edema, heat cramps, heat rash, heat tetany.
Prevention includes avoiding medications that can increase the risk of heat illness, gradual adjustment to heat, and sufficient fluids and electrolytes.[46][47]Vulnerable people with regard to heat illnesses include people with low incomes, minority groups, women (in particular pregnant women), children, older adults (over 65 years old), people with chronic diseases, disabilities and co-morbidities.[48]: 13 Other people at risk include those in urban environments (due to the urban heat island effect), outdoor workers and people who take certain prescription drugs.[48] Exposure to extreme heat poses an acute health hazard for many of the people deemed as vulnerable.[48][49]
Climate change increases the frequency and severity of heatwaves and thus heat stress for people. Human responses to heat stress can include heat stroke and hyperthermia. Extreme heat is also linked to low quality sleep, acute kidney injury and complications with pregnancy. Furthermore, it may cause the deterioration of pre-existing cardiovascular and respiratory disease.[50]: 1624 Adverse pregnancy outcomes due to high ambient temperatures include for example low birth weight and pre-term birth.[50]: 1051 Heat waves have also resulted in epidemics of chronic kidney disease (CKD).[51][52] Prolonged heat exposure, physical exertion, and dehydration are sufficient factors for the development of CKD.[51][52]Mortality
Health experts warn that "exposure to extreme heat increases the risk of death from cardiovascular, cerebrovascular, and respiratory conditions and all-cause mortality. Heat-related deaths in people older than 65 years reached a record high of an estimated 345 000 deaths in 2019".[48]: 9 More than 70,000 Europeans died as a result of the 2003 European heat wave.[53] Also more than 2,000 people died in Karachi, Pakistan in June 2015 due to a severe heat wave with temperatures as high as 49 °C (120 °F).[54][55]
Increasing access to indoor cooling (air conditioning) will help prevent heat-related mortality but current air conditioning technology is generally unsustainable as it contributes to greenhouse gas emissions, air pollution, peak electricity demand, and urban heat islands.[48]: 17Underreporting of fatalities
The number of heat fatalities is probably highly underreported. This is due to a lack of reports and to misreporting.[56] When considering heat-related illnesses as well, actual death tolls from extreme heat may be six times higher than official figures. This is based on studies of California[57] and Japan.[58]
Part of the mortality during a heat wave may be due to short-term forward mortality displacement. In some heat waves there is a decrease in overall mortality in the weeks after a heat wave. These compensatory reductions in mortality suggest that heat affects people who would have died anyway, and brings their deaths forward.[59]
Social institutions and structures influence the effects of risks. This factor can also help explain the underreporting of heat waves as a health risk. The deadly French heat wave in 2003 showed that heat wave dangers result from a combination of natural and social factors.[60] Social invisibility is one such factor. Heat-related deaths can occur indoors, for instance among elderly people living alone. In these cases it can be challenging to assign heat as a contributing factor.[61]
Heat index for temperature and relative humidity
Temperature Relative humidity
|
80 °F (27 °C) | 82 °F (28 °C) | 84 °F (29 °C) | 86 °F (30 °C) | 88 °F (31 °C) | 90 °F (32 °C) | 92 °F (33 °C) | 94 °F (34 °C) | 96 °F (36 °C) | 98 °F (37 °C) | 100 °F (38 °C) | 102 °F (39 °C) | 104 °F (40 °C) | 106 °F (41 °C) | 108 °F (42 °C) | 110 °F (43 °C) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 40% | 80 °F (27 °C) | 81 °F (27 °C) | 83 °F (28 °C) | 85 °F (29 °C) | 88 °F (31 °C) | 91 °F (33 °C) | 94 °F (34 °C) | 97 °F (36 °C) | 101 °F (38 °C) | 105 °F (41 °C) | 109 °F (43 °C) | 114 °F (46 °C) | 119 °F (48 °C) | 124 °F (51 °C) | 130 °F (54 °C) | 136 °F (58 °C) |
| 45% | 80 °F (27 °C) | 82 °F (28 °C) | 84 °F (29 °C) | 87 °F (31 °C) | 89 °F (32 °C) | 93 °F (34 °C) | 96 °F (36 °C) | 100 °F (38 °C) | 104 °F (40 °C) | 109 °F (43 °C) | 114 °F (46 °C) | 119 °F (48 °C) | 124 °F (51 °C) | 130 °F (54 °C) | 137 °F (58 °C) | |
| 50% | 81 °F (27 °C) | 83 °F (28 °C) | 85 °F (29 °C) | 88 °F (31 °C) | 91 °F (33 °C) | 95 °F (35 °C) | 99 °F (37 °C) | 103 °F (39 °C) | 108 °F (42 °C) | 113 °F (45 °C) | 118 °F (48 °C) | 124 °F (51 °C) | 131 °F (55 °C) | 137 °F (58 °C) | ||
| 55% | 81 °F (27 °C) | 84 °F (29 °C) | 86 °F (30 °C) | 89 °F (32 °C) | 93 °F (34 °C) | 97 °F (36 °C) | 101 °F (38 °C) | 106 °F (41 °C) | 112 °F (44 °C) | 117 °F (47 °C) | 124 °F (51 °C) | 130 °F (54 °C) | 137 °F (58 °C) | |||
| 60% | 82 °F (28 °C) | 84 °F (29 °C) | 88 °F (31 °C) | 91 °F (33 °C) | 95 °F (35 °C) | 100 °F (38 °C) | 105 °F (41 °C) | 110 °F (43 °C) | 116 °F (47 °C) | 123 °F (51 °C) | 129 °F (54 °C) | 137 °F (58 °C) | ||||
| 65% | 82 °F (28 °C) | 85 °F (29 °C) | 89 °F (32 °C) | 93 °F (34 °C) | 98 °F (37 °C) | 103 °F (39 °C) | 108 °F (42 °C) | 114 °F (46 °C) | 121 °F (49 °C) | 128 °F (53 °C) | 136 °F (58 °C) | |||||
| 70% | 83 °F (28 °C) | 86 °F (30 °C) | 90 °F (32 °C) | 95 °F (35 °C) | 100 °F (38 °C) | 105 °F (41 °C) | 112 °F (44 °C) | 119 °F (48 °C) | 126 °F (52 °C) | 134 °F (57 °C) | ||||||
| 75% | 84 °F (29 °C) | 88 °F (31 °C) | 92 °F (33 °C) | 97 °F (36 °C) | 103 °F (39 °C) | 109 °F (43 °C) | 116 °F (47 °C) | 124 °F (51 °C) | 132 °F (56 °C) | |||||||
| 80% | 84 °F (29 °C) | 89 °F (32 °C) | 94 °F (34 °C) | 100 °F (38 °C) | 106 °F (41 °C) | 113 °F (45 °C) | 121 °F (49 °C) | 129 °F (54 °C) | ||||||||
| 85% | 85 °F (29 °C) | 90 °F (32 °C) | 96 °F (36 °C) | 102 °F (39 °C) | 110 °F (43 °C) | 117 °F (47 °C) | 126 °F (52 °C) | 135 °F (57 °C) | ||||||||
| 90% | 86 °F (30 °C) | 91 °F (33 °C) | 98 °F (37 °C) | 105 °F (41 °C) | 113 °F (45 °C) | 122 °F (50 °C) | 131 °F (55 °C) | |||||||||
| 95% | 86 °F (30 °C) | 93 °F (34 °C) | 100 °F (38 °C) | 108 °F (42 °C) | 117 °F (47 °C) | 127 °F (53 °C) | Zdroj:https://en.wikipedia.org?pojem=Extreme_heat |